Three characteristics unique to electric power systems (system redundancy at nodes, the character of power flow, and emergency operations) are identified. Their importance in modeling power systems for the purpose of evaluating the effects of earthquakes on system performance is considered. Power systems utilize system redundancy to a greater extent than most other lifelines, such as water systems, or railroads. This is particularly true at system nodes which for power systems are contained in substations. The second characteristic that distinguishes power systems from other lifelines is the character of the flow in the system which is governed by Kirchhoff's equations. Thus, the topology of the network, the impedance of the branches, and the spatial distribution of the loads and sources determines the flow in the branches. The implications of the preceding two characteristics on systems operations of an earthquake-damaged system is that: (1)The configuration of the network will be changed as a result of system damage that may cause some branches to become overloaded; and (2)the flexibility in configuring the system must be used to match loads to power line capacity.